Method for solution growth of gallium arsenide and gallium phosphide



' M. B. PANISH ETAL METHOD FOR SOLUTION GROWTH OF GALLIUM I ARSENIDE AND GALLIUM PHOSPHIDE Filed July 17, 1967 v ,NVEWORS M. a. PAN/SH ATTORNEY United States Patent US. Cl. 148-15 6 Claims ABSTRACT OF THE DISCLOSURE Solution growth of single crystal gallium arsenide or gallium phosphide upon gallium arsenide and gallium phosphide substrate crystals involves the use of capillary action to form a thin film of molten gallium between two crystal wafers, epitaxial growth occurring during a subsequent cooling cycle.

This invention relates to a technnique for the growth of Group IIIa-Va semiconductive compositions. More particularly, the present invention relates to a technique for the growth of single crystal gallium arsenide and gallium phosphide by solution growth.

Recently, considerable interest has been generated in a class of electroluminescent devices utilizing the arsenide or phosphide of gallium, so creating a need for the effective growth of device grade materials suitable for this purpose. Heretofore, the most common procedure for effecting this end involved the so-called solution growth techniques wherein crystalline materials are grown from solution either by cooling the saturated liquid phase or by tipping a saturated liquid phase upon a seed crystal and, subsequently, cooling. Although crystalline materials grown in accordance with such techniques have proven superior to materials obtained by other well-known procedures, workers in the art have attempted to reduce growth time and to simplify equipment requirements.

In accordance with the present invention these ends are attained by means of a novel solution growth technique wherein capillary action is relied upon to form a thin film of molten gallium between two crystal wafers, epi taxial growth occurring during a subsequent cooling cycle. The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawing wherein:

The figure is a cross-sectional view of an apparatus suitable in the practice of the present invention.

With reference now to the growth process, the first step involves preparing at least two waters of gallium arsenide or gallium phosphide. This end may be attained by any well-known prior art procedure as, for example, by solution growth, vapor growth and so forth. It will be appreciated that any of the well-known donors or acceptors may be added in this initial growth period in order to control the conductivity type of the substrate crystal.

Suitable wafers having been obtained, the next step in the inventive procedure involves polishing the crystal faces fiat by any conventional lapping technninque. Thereafter, the crystals are etched in order to rid the surfaces of all traces of undesirable impurities and to eliminate surface damage. To this end, the crystals are advantageously etched in any suitable etchant, such as a chlorine-methanol etch. Etching with suitable masking means is continued for a time period sufiicient to assure the growth of several feet or appendages upon one of the crystalline wafers, such appendages serving to provide a space between the wafers during the growth processes. The wafers so prepared are then placed in the form of a sandwich in a suitable chamber of the type shown in the figure.

:Referring now more particularly to the figure, there is shown an exemplary apparatus suitable for the practice of the subject invention. Shown in the figure is a sealed chamber 11 having disposed therein a strip heater 12 bearing a sandwich structure comprising a pair of parallel semicondutive wafers 13 and 14 separated from each other by means of appendages 15. Chamber 11 also includes means 16 for admitting a gas into a system and means 17 for removing the gas. Also included within chamber 11 is a chuck 18 attached to a micromanipulae tor 18A, a rod 19 of the semiconductive material to be grown being supported by chuck 1'8, and a droplet of molten gallium 20. Doping of the grown layer is attained by adding the desired dopant to droplet 20. An A-C source 21 provides high current and low voltage to strip heater 12 via a step down transformer 22.

In the operation of the process, an inert gas such as helium is intially flushed through the system and thereafter hydrogen is flowed therethrough. Next, the strip heater is heated to a temperature within the range of 700-900 C. The pendant gallium ball 20, containing any desired dopants, is then contacted with the strip heater near the sandwich and a portion of the support rod dissolves therein. The pendant ball is then lifted from the heater by means of the micromanipulator and the temperature increased approximately 50 C. so that the range of operating temperatures varies from 750950 C. Studies have revealed that at temperatures in excess of the 950 C. maximum the samples decompose, whereas the use of temperatures less than 750 C. are inadequate to effect the desired capillary action.

The pendant droplet [which had been saturated with either gallium arsenide or gallium phosphide at the lower temperature is now placed upon the protruding portion of the lower wafer as shown in the figure, and the molten gallium rapidly fills the volume defined by the space gradient between the wafers by capillary action while dissolving a small amount of additional gallium arsenide or gallium phosphide.

Growth of the desired gallium arsenide or gallium phosphide layer is effected by maintaining the highest temperature for a time period of approximately one minute or less and then initiating a controlled cooling program of approximately C(per minute, or by rapid cooling to room temperature by completely shutting off the power to the strip heater. Studies of the resultant films indicate that the dissolved gallium arsenide or gallium phosphide deposits as a gallium arsenide or gallium phosphide layer on the surface of the upper and lower wafers.

An example of the application of the present invention is set forth below. It is intended merely as an illustration, and it is to be appreciated that the methods described may be varied by one skilled in the art without departing from the spirit and scope of the invention.

EXAMPLE Two waters of boat-grown gallium arsenide, obtained from commercial sources were polished fiat by lapping with 305 Carborundum abrasive and etched with a chlorine-methanol solution, one of the wafers being etched in such manner that it had four feet or shims, approximately 2 mils high. The resultant wafers were next placed upon a strip heater in an apparatus similar to that shown in the figure in the form of a sandwich.

Following, a small rod of gallium arsenide, approximately 40 mil x 40 mil x 1 cm. was supported from an adjustable chuck within the heater housing of the apparatus, the chuck being attached to a micromanipulator being mounted outside the system. Next, a droplet of liquid gallium was placed upon the end of the gallium arsenide rod and held in position by means of surface tension.

Next, the system was sealed, flushed with helium, and a continuous fiow of hydrogen introduced thereto. The temperature of the heater was then elevated to 800 C. and the pendant gallium droplet touched thereto at a point near the sandwich, so resulting in dissolution of a portion of the gallium arsenide rod. The droplet was then lifted from the heater strip and the temperature elevated to 850 C., at which point the pendant droplet was placed on a protruding portion of the lower wafer. The gallium rapidly filled the space between the upper and lower wafers by capillary action while dissolving a small amount of gallium arsenide. The temperature was maintained at 850 C. for about one minute and cooling initiated by shutting off the power to the strip heater. Examination of the resultant layers revealed dense single crystal gallium arsenide films approximately 0.3 mil on the top wafer and approximately 0.2 mil on the bottom wafer.

What is clamed is:

1. A method for the solution growth of epitaxial films of a material selected from the group consisting of gallium arsenide and gallium phosphide upon a substrate crystal which comprises the steps of (1) positioning at least two waters of said material parallel to and in spaced relationship to each other in a sealed chamber; (2) heating a droplet of gallium containing the said material to a temperature within the range of 750950 C.; (3) contacting at least one of said wafers therewith upon an internal surface whereby said droplet migrates by capillary action across the volume defined by the space between said wafers; and (4) cooling the resultant assembly to room temperature, whereby an epitxaial film of said material is deposited upon each of said wafers.

2. A method in accordance with the procedure of claim 1 wherein said material is gallium arsenide and said sub strate crystal is gallium arsenide.

3. A method in accordance with the procedure of claim 1 wherein said material is gallium phosphide and said substrate crystal is gallium phosphide.

4. A method for the solution growth of epitaxial films of a material selected from the group consisting of gallium arsenide and gallium phosphide upon at least two substrate crystals which comprises: (1) positioning the substrates of the material parallel to and in spaced relationship to each other in a sealed chamber; (2) contacting a droplet of gallium with a supply of the material to be grown; (3) heating said droplet to a temperature within the range of 700900 C. to dissolve a portion of said supply to form a gallium, droplet containing the material to be grown; (4) further heating said gallium droplet containing the material to be grown to a temperature within the range of 750-950" C.; (5) contacting at least one of the substrates with said material containing gallium droplet upon an internal surface whereby said material containing droplet migrates by capillary action across the volume defined by the space between the substrates; and (6) cooling the resultant assembly to room temperature to simultaneously deposit the material on the substrates.

5. The method as defined in claim 4 wherein said material is gallium arsenide and said substrate crystals are gallium arsenide.

6. The method as defined in claim 5 wherein said material is gallium phosphide and said substrate crystals are gallium phosphide.

References Cited UNITED STATES PATENTS 3,351,502 11/1967 Rediker 148-177 3,360,406 12/1967 Sumski 1481.6 3,429,818 2/1969 Di Benedetto 252-629 OTHER REFERENCES Mlavsky, A. 1., et al.: J. Applied Physics, vol. 34, No. 9, 1963, pp. 28852892. V

L. DEWAYNE RUTLEDGE, Primary Examiner W. S. SABA, Assistant Examiner US. Cl. X.R. 

